This research program involves studies of the application of mass spectometry to molecular structure determination and analysis applicable to biomedical research. A "Probability Based Matching" system incorporating data weighting and reverse searching has been developed to retrieve mass spectra from a large data base. Unknown mass spectra can now be characterized by a combination of this system and our "Self-Training Interpretive and Retrieval System" on the Cornell IBM-370/168 computer which is accessible by a local phone call over the TYMNET computer network. High-speed liquid chromatography can be monitored by direct introduction of solutions into a chemical ionization mass spectrometer. Collisional activation analysis has made possible the characterization of the structures of a substantial number and variety of ions. BIBLIOGRAPHIC REFERENCES: M.A. Baldwin, F.W. McLafferty, and D. M. Jerina, Rearrangements of Toluene and Cycloheptatriene Cations, J. Am. Chem. Soc., 97, 6169 (1975). P.F. Bente, III, F.W. McLafferty, D.J. McAdoo, and C. Lifshitz, Internal Energy of Product Ions Formed in Mass Spectral Reactions. The Degrees of Freedom Effect, J. Phys. Chem., 79, 713 (1975).